This is temporary number for people who want to stay in Norway up to six months. It takes approximately six weeks to get it. Without the number you will not get a contract at work and it means you will not be able to create a bank account. The best is to register at selfservice.udi.no before you leave to Norway. It can take even two months to get in touch with someone from Skattekontoret (tax office). If you want to stay in Norway longer than six months then you need to get this number again. The number has to be renewed annually if you are living in Norway.